Preloaded tie rod end assembly

ABSTRACT

A preloaded tie rod assembly for a motor vehicle steering system and the method for making the assembly is disclosed. The tie rod end is made by positioning first and second frangible bearings against the ball of a ball stud and enclosing the ball and bearings in first and second housings each of which has a socket part and a stem part. A plastically deformable element is also situated within the socket formed by the two socket parts. The two housings are held together under a compressive load while their abutting edges are butt welded. The imposition of this load during the welding operation causes the frangible bearings to each fracture into a plurality of self-aligning bearing pieces. The deformable element is plastically deformed by exerting a force on the ball stud whereby a portion of the preload of the joint is relieved. The preload is relieved to the extent necessary to bring the frictional resistance to rotation of the ball stud within a prescribed torque range.

BACKGROUND OF THE DISCLOSURE

In order to provide a steering linkage system for a motor vehicle thatoperates in an optimum manner, it is necessary to have tie rod endassemblies each of which has a frictional resistance to joint movementthat is within prescribed operating limits. Frictional resistance thatis either above or below the desired range may exhibit undesirableeffects.

While the steering will function for its intended purpose oftransmitting a steering force from the steering wheel to the steerableroad wheels, the vehicle operator may find that the steering does nothave a desired precision "feel" or that excessive vibration andharshness may be transmitted from the road wheels through the linkage tothe steering wheel.

The present invention provides a preloaded tie rod end assembly for amotor vehicle steering linkage system that is characterized by itsunique construction and method of manufacture which permits precisecontrol of the preload of the joint while being relatively inexpensiveto fabricate.

BRIEF SUMMARY OF THE DISCLOSURE

In the presently preferred form of a preloaded tie rod end assemblyaccording to this invention, first and second housing parts each have asocket portion and a stem portion. A plastically deformable lead washeris fitted in the socket portion of the first housing. A first annularfrangible bearing is positioned in the same socket part with the ball ofa ball stud in engagement with the bearing. A second bearing engages theball and the second housing has its socket part enclosing the secondbearing.

The first and second housing parts have abutting edges and the parts aresecured together by butt welding the edges at the same time acompressive load is imposed upon the two housing parts. The compressioncauses each of the bearings to each fracture into a plurality ofcircumferentially spaced apart bearing pieces. At this point in themanufacturing operation after the welding step is completed, the jointhas a preload that exceeds a predetermined desired amount. An axialforce is then exerted on the ball stud causing the deformable element toplastically deform and this deformation relieves a portion of thepreload. The element is deformed by an amount necessary to bring thefrictional resistance to rotation of the ball stud within the desiredpredetermined range.

The subject matter of the disclosure of this patent relates, in ageneral way, to the subject matter of the disclosures of United StatesPat. applications Ser. No. 593,809 for "Suspension Arm and JointAssembly" and Ser. No. 593,810 for "Tie Rod End", both filed July 7,1975 by W. D. Allison, the patentee hereof. Each of these applicationsdiscloses a fragmented bearing means.

BRIEF DESCRIPTION OF THE DRAWINGS

The many objects and advantages of a preloaded tie rod end assembly thatis made in accordance with this invention will become apparent uponconsideration of the following detailed description and the accompanyingdrawings, in which:

FIG. 1 is a side view in section of a new tie rod end construction;

FIG. 2 is a top plan view of the tie rod end of FIG. 1;

FIG. 3 is an end elevational view of the stem end of the tie rod end;

FIG. 4 is a sectional view of one of the bearing means of the tie rodend; and

FIG. 5 is a bottom plan view of the bearing of FIG. 4 taken in thedirection of arrows 5--5.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to the drawings wherein the presently preferred embodimentof this invention is illustrated, FIG. 1 shows the construction of apreloaded tie rod end assembly 10. The tie rod end 10 has a lowerhousing 12 with a socket part 14 and a stem part 16 and an upper housing18 with a socket part 20 and a stem part 22.

A lead washer 24 is positioned at the base of the socket part 14. Asteel washer 26 is fitted on top of the lead washer 24. A lowerfrangible bearing 28 rests on the steel washer 26.

A ball stud 30 has a ball portion 32 that rests on the bearing 28. Theshank 34 of the stud 30 extends upwardly through an opening 36 in theupper socket part 20. An upper bearing 38 is fitted in the upper socketpart 20 in engagement with the ball 32.

The bearings 28 and 38 are of identical construction. Referring to FIGS.4 and 5, the configuration of the bearing 38 is shown prior to itsinstallation into the upper socket part 20. Bearing 38 is generallyannular with a cylindrical outer surface 40 and a partially sphericalinner bearing surface 42 for slidable engagement with the ball 32. Thebearing 38 is provided with a series of equally spaced apart slots 44,46, 48 and 50. These slots divide the bearing into four bearingsegments. Slot 44 extends completely through the bearing materialwhereas slots 46, 48 and 50 extend only partially through the materialso that tie bars 52, 54 and 56 are provided to interconnect the foursegments of the bearing 38.

The bearing 38 is molded of powdered bronze and is frangible. The tiebars 52, 54 and 56 holding the bearing segments together are easilyfractured under a load as will become apparent.

The stem portions 16 and 22 of the housing parts 12 and 18 combine toform a hollow stem that is internally threaded at 58 for attachment toan element of a steering linkage system. A rubber plug 60 is situated atthe inner end of the hollow stem and functions as a seal to retainlubricant within the joint 10. A boot seal (not shown) may be providedin sealed engagement with the ball stud shank 34 and upper housing 20 inorder to close the opening 36 and prevent the entry of contaminants intothe interior of the tie rod end 10.

METHOD OF MANUFACTURE

The preloaded tie rod end assembly 10 is manufactured by forming theupper and lower housing parts 12 and 18 as illustrated. The lead andsteel washers 24 and 26 together with the lower bearing 28 arepositioned in the socket part 14 of the lower housing 12. The ball 32 ispositioned against the bearing 28, the second bearing 38 is positionedagainst the ball 32 and finally the upper housing part 18 is placed withits socket part 20 over the bearing 38 and its stem portion 22 over stemportion 16 of the lower housing 12.

The housing parts 12 and 18 have peripheral edges that are positioned inabutting relationship. The housing parts 12 and 18 are compressedtogether at the same time the seam formed by the abutting edges of thehousing parts is butt welded. It will be noted from the drawings thatthe welded seam 62 bulges outward as a result of the compressive load.This load is transmitted to the upper and lower bearings 28 and 38causing their tie bars to fracture. As a result, each of the bearings 28and 38 becomes a series of circumferentially spaced apart bearingelements and these bearing elements align themselves with respect to theupper and lower socket parts 14 and 20 and with respect to the ball 32.Due to the self-aligning feature, close tolerance control in themanufacture of the upper and lower housings 12 and 18 and of the ball 32is not required.

The welding of the seams 62 while the housings 12 and 18 are undercompression, in addition to fracturing the bearings 28 and 38, willimpose a preload that exceeds the amount desired for the finished joint.That is, the torque required to overcome the frictional resistance torotation of the stud 30 about its own axis or to pivot the stud aboutthe center of the ball 32 will be greater than a desired predeterminedamount. In order to reduce the preload so that it falls within thedesired range, an axial force in the downward direction is exerted onthe stud 30. The load imposed on the stud 30 is sufficiently great tocause partial plastic deformation of the lead washer 24. The axial loadis imposed in increments and the frictional resistance to rotation ofthe ball stud 30 is noted between each increment. Plastic deformation ofthe washer 24 will relieve a portion of the preload of the joint and theaxial force on the stud 30 is applied to the extent necessary to bringthe frictional resistance to rotation of the stud into the desiredtorque range. For a typical vehicle steering application that rangewould be about 8 to 15 inch pounds.

The interior of the stem of the tie rod 10 is threaded at 58 toaccommodate attachment to a steering linkage element. As also shown, theshank 34 of the stud 30 is constructed to be connected to anotherelement of a steering system. The assembly or manufacture of the tie rodend 10 is completed by inserting the rubber plug 60 and placinglubricant within the socket parts 12 and 14. Finally, a boot seal (notshown) is positioned over the shank 38 in engagement with the uppersocket part 20.

SUMMARY

The preloaded tie rod end assembly of this invention is characterized byits simplicity of construction and ease of manufacture. The method bywhich the preload is established assures a finished joint havingfrictional resistance to movement within the desired specified range. Inaddition, the self-aligning construction of the bearings permits the useof stamped housing parts not requiring close tolerances.

The foregoing description presents the presently preferred embodiment ofthis invention. Modifications and alterations may occur to those skilledin the art that will come within the scope and spirit of the followingclaims.

I claim:
 1. A tie rod end assembly comprising a housing having first andsecond housing parts;each of said housing parts having a socket portionand a stem portion; said first and second housing parts having abuttingedges; a weldment bead interconnecting said abutting edges of said firstand second housing parts; said stem portions of said first and secondhousing parts defining a stem constructed for attachment to a threadedelement of a vehicle steering system; said socket portions of said firstand second housing parts forming a socket cavity and having an axistransverse to said stem; first and second axially spaced bearing meansdisposed in said cavity; each of said bearing means comprising aplurality of circumferentially arranged discrete bearing pieces; a ballstud having a ball slidably engaging said bearing pieces of said firstand second bearing means and a shank extending exteriorly from saidsocket cavity; said bearing pieces of said first bearing means and saidsecond bearing means being in direct abutting engagement with said firsthousing part and said second housing part, respectively.
 2. A tie rodend assembly comprising a housing having first and second sheet metalstamped housing parts;each of said housing parts having a socket portionand a stem portion; said first and second housing parts having abuttingedges; a weldment bead interconnecting said abutting edges of said firstand second housing parts; said stem portions of said first and secondhousing parts defining a stem constructed for attachment to a threadedelement of a vehicle steering system; said socket portions of said firstand second housing parts forming a socket cavity and having an axistransverse to said stem; first and second axially spaced bearing meansdisposed in said cavity; each of said bearing means comprising aplurality of circumferentially arranged discrete bearing pieces; a ballstud having a ball slidably engaging said bearing pieces of said firstand second bearing means and a shank extending exteriorly from saidsocket cavity; said bearing pieces of said first bearing means and saidbearing pieces of said second bearing means being in direct abuttingengagement with said first housing part and said second housing part,respectively; a nonelastic plastically deformable element disposed insaid socket cavity; load transfer means operatively interposed betweensaid ball stud and said plastically deformable element; said loadtransfer means being constructed to transfer a load of sufficientmagnitude to deform said deformable element from said ball stud to saiddeformable element; said plastically deformable element having a loweryield strength than said ball stud, said load transfer means or saidhousing parts.
 3. A tie rod end assembly comprising a housing havingfirst and second sheet metal stamped housing parts;each of said housingparts having a socket portion and a stem portion; said first and secondhousing parts having abutting edges; a weldment bead interconnectingsaid abutting edges of said first and second housing parts; said stemportions of said first and second housing parts defining a stem havinginternal threads for attachment to an element of a vehicle steeringsystem; said socket portions of said first and second housing partsforming a socket cavity and having an axis transverse to said stem;first and second axially spaced bearing means disposed in said cavity;each of said bearing means comprising a plurality of circumferentiallyarranged discrete bearing pieces; a ball stud having a ball slidablyengaging said bearing pieces of said first and second bearing means anda shank extending exteriorly from said socket cavity; said bearingpieces of said first bearing means and said bearing pieces of saidsecond bearing means being in direct abutting engagement with said firsthousing part and said second housing part, respectively; a nonelasticplastically deformable element disposed in said socket cavity; loadtransfer means operatively interposed between said ball stud and saidplastic deformable element; said load transfer means being constructedto transfer a load of sufficient magnitude to deform said deformableelement from said ball stud to said deformable element; said plasticallydeformable element having a lower yield strength than said ball stud,said load transfer means or said housing parts. said plastic deformableelement having a thickness in said tie rod end assembly that is lessthan its thickness prior to assembly in said tie rod end assembly.